Infinitely variable multi-turn potentiometer



March 28, 1967 K. FRANK 3,311,860

INFINITELY VARIABLE MULTI-TURN POTENTIOMETER Filed Jan. 9, 1964 FIG 5 FIG 3 FIG 4 INVENTOR. KARL F. FRANK United States Patent 3,311,860 INFINITELY VARIABLE MULTI-TURN PGTENTIOMETER Karl F. Frank, Garden City, N.Y., assignor to Micro Balancing Incorporated, Garden City Park, N.Y. Filed Jan. 9, I964, Ser. No. 336,715 2 Clairns. (Cl. 338-145) This invention relates to infinitely variable potentiometers and more particularly to such potentiometers of low resistance value.

Conventional potentiometers generally have a coil of I resistance wire and an arm riding over turns of the coil. These potentiometers are not infinitely variable since they vary resistance in steps from turn to turn. Infinitely variably potentiometers require the pick-off contact to ride along the entire length of the resistance wire.

Some infinitely variable potentiometers are made of a straight piece of resistance wire with a sliding contact. However, these devices are large and cumbersome and provide poor heat dissipation. To provide a compact assembly the resistance wire is preferably a coil and the contact must ride along its length. This provides diificult design problems in order to provide a smooth motion and long wearing parts which have an infinitely variable adjustment along the length of the resistance wire and dissipate the heat generated in the resistance Wire.

The present invention solves these problems and provides a. variable potentiometer comprising a hollow case, a nut fixedly mounted in said case, and connected to one terminal, said nut having internal threads, a partially hollow mandrel, a coil of resistance wire mounted on the mandrel, the turns of the coil riding in the threads so that as the mandrel is turned it will slide axially relative the nut. A spring fixed point contact is fixedly connected to the nut and one attached fixed terminal.

The mandrel is rotated by the means of a shaft of insulating material. The circuit is completed through the resistance coil, one end of the resistance coil being connected to the mandrel. The mandrel is insulated from the coil at all other points. A sliding contact slip ring is provided bearing against the mandrel by spring pressure and the circuit is completed through the sliding contacts through a woven copper cover on the spring to a second external contact. The resistance of the woven copper cover of the spring is very low and further is a constant value, so that precision readings may be obtained from the resistance of the resistance wire which is within the circuit.

Accordingly, a principal object of the invention is to provide new and improved infinitely variable potentiometer means.

Another object of the invention is to provide new and improved infinitely variable potentiometer means of low resistance.

Another object of the invention is to provide new and improved precision potentiometer means.

Another object of the invention is to provide new and improved infinitely variable potentiometer means of small size.

Another object of the invention is to provide new and improved infinitely variable potentiometer means comprising a rotatable coil of the resistance wire in close contact with the mandrel for heat dissipation which engages the threads with a fixed nut, said nut having a fixed point contact pick-oil.

Another object of the invention is to provide a new and improved infinitely variable potentiometer comprising, a hollow case, a conductive nut fixed inside said case, said nut having internal threads, a partially hollow conductive mandrel with an insulated cover on its outer surface,

a coil of resistance wire'mounted on said insulated surface of said mandrel, the turns-of said coil riding in said threads of said nut, one end of said coil being electrically connected to said mandrel, a spring fixed point contact mounted in said nut, said fixed point contact riding on said wire, means to rotate said mandrel relative said nut and contact, a slip ring contact member riding on said mandrel, a pair of external terminals on said case one of said terminals being connected to said slip ring the other of said terminals being connected to said fixed nut.

These and other objects of the invention will be apparent from the following specification and drawings of which:

FIGURE 1 is a sectional view of an embodiment of the invention.

FIGURE 2 is an end view of an embodiment of FIG- URE 1.

FIGURE 3 is a sectional view of the mandrel or coil form of the embodiment of FIGURE 1;

FIGURE 4 is an end View of FIGURE 3.

FIGURE 5 is an end view of the nut of the embodiment of FIGURE '1.

Referring to FIGURE 1, there is shown a sectional view of the invention comprising, a hollow case 1, which is preferably cylindrical and constructed of insulating material such as a plastic. Attached to the ends of the case 1 are two end pieces 2 and 3, the piece 3 being apertured to receive a rotatable shaft which will be described. A conductive nut 4 is fixedly mount-ed in the casing preferably by screws and the nut has internal threads. A partially hollow mandrel or wire form 5 is mounted inside the nut. The wire form has an insulation cover 6 on its external surface. This insulation cover may be a very thin coating of Teflon or other insulation material.

Wound on the external surface of the mandrel or wire form 5 is a coil of resistance wire 7, the coil having a pitch equal to the threads of the nut 4. The coil 7 engage-s the thread of the nut 4, so that when the mandrel is rotated the coil will move axially relative the nut 4.

Also, referring to FIGURE 5, the nut 4 has a recess portion and a pair of slots 8 and 9. Mounted in the slots is a spring contact 11 which has a single projection 11 which constitutes a single point contact which rides along the resistance wire coil 7.

The inside of the mandrel or wire form 5 is hollowed out and the bottom of the mandrel contains a square aperture 5a, FIGURE 4. The mandrel is adapted to be rotated by means of a rotatable shaft '12 Which is mounted in the cover 3 by means of the nuts 13 and '14 which engage the threaded sleeve 15, so that it is constrained from any axial movement. The internal end 12 of the shaft 12 has a square shape which passes through the square aperture in the wire form or mandrel 5. At the end of the shaft 12' is a stop washer 16.

Mounted about the shaft in a coaxial manner is a sliding contact 17 which acts as a slip ring contact. It has three or more silver contacts which ride on the surface 1 8 of the conductive wire form 5. The slip ring 17 is pressed against the wire form 5 by means of a spring 19 which is mounted about the shaft 12 in coaxial relation, the other end of spring bearing against the inside of the cover 3. A copper woven wire cover 26 is mounted on the spring for the purpose of completing the circuit from the slip ring 17 to the terminal 20. The other external contact 21 is also mounted in the case 1 and is connected to the nut 4. Therefore, a circuit is completed from the contact 20, through the woven copper wire cover on the spring 19 to the slip ring 17. The circuit is then completed through the wire form 5 to the coil or resistance wire 7 which is connected to the wire form at the point 25. The circuit is then completed through the coil 7 to the single point contact 11, then through the nut to the external terminal 211. The variable resistance is that of the coil between the single point contact 11 and the point 25. The other components in the circuit have negligible resistance and furthermore they are constant.

A stop washer 27 is mounted on one end of the wire form to limit the motion in the direction to the right in FIGURE 1. The motion in direction to the left is stopped by the washer '16 bearing against the wire form 5.

Therefore, rotation of the shaft 12 will cause the Wire form to move axially to thereby cause the point contact 11 to move along the entire length of the resistance wire to provide infinitely variable resistance. The amount of resistance for particular applications may be varied by changing the size of the resistance wire and this will necessitate changing the size of the threads in nut 4. The resistance wire must be carefully wound so that it has the same pitch as the threads in nut 4. The resistance wire may be made as small a diameter as will operably engage threads in the nut 4 and of as large a diameter as desired.

The resistance wire may be of any suitable resistance wire depending upon the amount of resistance desired. It may be, for instance nickel-alloy resistance wire with a low temperature coefficient.

FIGURE 3 shows a sectional view of the wire form or mandrel 5 which has groove 5 for receiving the resistance wire 7. The resistance wire is a bare wire and the external surface of the mandrel 5 is covered with an insulation 6 which may be a thin coating of Teflon or other insulation.

Referring to FIGURE 4, the aperture through the mandrel 5 is a square aperture 5a, which is adapted to accommodate the square portion 12' of the shaft. The shaft portion 12 is preferably of plastic such as Bakelite or some other insulation material.

FIGURE 5 shows a detail view of the nut 4-.

In' a particular embodiment which was one halt the size of FIGURE 1, the diameter of the resistance wire was 0.032 inch diameter and provided a resistance range from 0.02 ohm to 2 ohms that is a ratio of 100 to 1, with a 5 watt heat dissipation capacity. By changing the diameter :of the resistance wire and/ or the length of the coil,

the amount of resistance and power rating may be changed depending upon the particular application.

Many modifications may be made by those who desire to practice the invention without departing from the scope thereof which is defined by the following claims.

I claim:

1. An infinitely variable potentiometer comprising:

a hollow case,

a conductive nut fixed inside said case, said nut having internal threads,

a partially hollow conductive mandrel with an insulated cover on its outer surface,

a coil of resistance wire mounted on said insulated surface of said mandrel, the turns of said coil having the same pitch as and riding in said threads of said nut,

one end of said coil being electrically connected to said mandrel,

a spring single point contact mounted in said nut, said single point contact riding on said wire,

mean-s to rotate said mandrel relative to said nut and contact comprising,

a non-conductive shaft rotatably mounted in said case and extending through said mandrel and rotatably connected to said mandrel but' permitting axial movement of said mandrel relative to said shaft,

a second sliding contact member mounted coaxially about said shaft and riding on an interior conductive surface on said mandrel,

a spring mounted coaxially about said shaft and bearing against said second contact member to hold said contact member in contact with said mandrel,

a woven copper cover on said spring,

a pair of external terminals on said case one of said terminals being connected to one end of said copper cover and the other of said terminals being connected to said fixed nut,

whereby a circuit is completed from said one terminal through said copper cover, said second sliding contact, said mandrel, a portion of said resistance coil, and said single point contact mounted on said nut to said other terminal.

2. An infinitely variable potentiometer comprising,

a hollow cylindrical case of insulating material,

a conductive nut fixed inside said case, said nut having internal threads,

a partially hollow conductive mandrel with an insulated cover on its outer surface,

a coil of resistance wire mounted on said insulated surface of said mandrel, the turns of said coil having the same pitch as and riding in said threads of said nut,

one end of said coil being electrically connected to said mandrel, v

a spring single point contact mounted in said nut, said single point contact riding on said wire,

means to rotate said mandrel relative to said nut and contact comprising,

a shaft rotatably mounted in said case and extending through said mandrel and connected to rotate said mandrel but permitting axial movement of said mandrel relative to said shaft, said shaft being insulated from said mandrel,

a slip ring member mounted coaxially about said shaft and riding on an interior conductive surface of said mandrel, 7

spring means mounted coaxially about said shaft and bearing against said slip ring member to hold said slip ring in contact with said mandrel,

a pair of external terminals on said case one of said terminals being connected to one end of said spring means and the other of said terminals being connected to said fixed n-ut,

whereby a circuit is completed from said one terminal through said spring means, said slip ring, said mandrel, a portion of said resistance coil, and said single point contact mounted on said nut to said other terminal.

References Cited by the Examiner UNITED STATES PATENTS 1,780,600 11/1925 Pullwitt 338-143 FOREIGN PATENTS 265,356 2/1927 Great Britain.

ANTHONY BARTIS, Primaly Examiner.

RICHARD M. WOOD, Examiner.

J. G. SMITH, Assistant Examiner. 

1. AN INFINITELY VARIABLE POTENTIOMETER COMPRISING: A HOLLOW CASE, A CONDUCTIVE NUT FIXED INSIDE SAID CASE, SAID NUT HAVING INTERNAL THREADS, A PARTIALLY HOLLOW CONDUCTIVE MANDREL WITH AN INSULATED COVER ON ITS OUTER SURFACE, A COIL OF RESISTANCE WIRE MOUNTED ON SAID INSULATED SURFACE OF SAID MANDREL, THE TURNS OF SAID COIL HAVING THE SAME PITCH AS AND RIDING IN SAID THREADS OF SAID NUT, ONE END OF SAID COIL BEING ELECTRICALLY CONNECTED TO SAID MANDREL, A SPRING SINGLE POINT CONTACT MOUNTED IN SAID NUT, SAID SINGLE POINT CONTACT RIDING ON SAID WIRE, MEANS TO ROTATE SAID MANDREL RELATIVE TO SAID NUT AND CONTACT COMPRISING, A NON-CONDUCTIVE SHAFT ROTATABLY MOUNTED IN SAID CASE AND EXTENDING THROUGH SAID MANDREL AND ROTATABLY CONNECTED TO SAID MANDREL BUT PERMITTING AXIAL MOVEMENT OF SAID MANDREL RELATIVE TO SAID SHAFT, A SECOND SLIDING CONTACT MEMBER MOUNTED COAXIALLY ABOUT SAID SHAFT AND RIDING ON AN INTERIOR CONDUCTIVE SURFACE ON SAID MANDREL, A SPRING MOUNTED COAXIALLY ABOUT SAID SHAFT AND BEARING AGAINST SAID SECOND CONTACT MEMBER TO HOLD SAID CONTACT MEMBER IN CONTACT WITH SAID MANDREL, A WOVEN COPPER COVER ON SAID SPRING, A PAIR OF EXTERNAL TERMINALS ON SAID CASE ONE OF SAID TERMINALS BEING CONNECTED TO ONE END OF SAID COPPER COVER AND THE OTHER OF SAID TERMINALS BEING CONNECTED TO SAID FIXED NUT, WHEREBY A CIRCUIT IS COMPLETED FROM SAID ONE TERMINAL THROUGH SAID COPPER COVER, SAID SECOND SLIDING CONTACT, SAID MANDREL, A PORTION OF SAID RESISTANCE COIL, AND SAID SINGLE POINT CONTACT MOUNTED ON SAID NUT TO SAID OTHER TERMINAL. 